With the advancement of information technology, information of magazines, newspapers, in-house documents, and the like are digitized to provide image data, which is then stored in electronic document files on electronic document servers. In order to view electronic document images (hereinafter simply referred to as “electronic documents”) stored on the electronic document servers, images are generally displayed on display screens at user terminals via various communication networks, including LAN (Local Area Network) and WAN (Wide Area Network).
As a method for transmitting images in such cases, a progressive (progressive) transmission technique is commonly used. With the progressive transmission technology, during the transmission of an image, the image is displayed gradually sharper (by gradually increasing the resolution) through several steps.
Relevant technologies using such a progressive transmission technique will be described with reference to particular documents.
Japanese Unexamined Patent Publication (JP-A) No. 2000-50261 (hereinafter referred to as “Patent Document 1”) discloses the following technology. A user specifies an important area in an image in advance. An image specified as an important area is transmitted prior to the images of areas other than the important area.
Japanese Unexamined Patent Publication (JP-A) No. 11-242654 (hereinafter referred to as “Patent Document 2”) discloses the following technology. A document image (document image) specified by a user is separately transmitted at two-stage resolutions through the use of a layout structure in the document. That is, a layout structure in the document image is identified and a layout object that is more likely to be referred to by the user is transmitted to the user terminal at a high resolution. On the other hand, a layout object that is less likely to be referred to by the user is transmitted to the user terminal at a low resolution.
Japanese Unexamined Patent Publication (JP-A) No. 2001-148802 (hereinafter referred to as “Patent Document 3”) discloses the following technology. In order to prevent transfer failure of image data due to battery depletion of a digital camera, the up-time based on a battery remaining capacity is determined. Based on the determined up-time and a data transmission speed, a file size (the amount of data) that can be transmitted is determined. The resolution level of the image file is determined in accordance with the determined transmittable file size and the image is transmitted at the determined resolution level.
Electronic documents to be viewed in an electronic-document viewing system include not only individual electronic documents and electronic magazines but also a group of search-result's electronic documents that are found through keyword searching. Since the amount of data for an electronic document is enormous, much time is required to download the entire electronic document to a user terminal. In general, users wish to check what are contents of electronic documents they are receiving like or where desired contents exist, as quickly as possible. That is, in the electronic-document viewing system, it is required that necessary electronic documents be downloaded as quickly as possible while minimizing inconvenience to the users.
For example, in the technology disclosed in Document 1, image information of the user-specified important area is progressively transmitted prior to image information of the other areas. This technology, however, cannot control the resolution level of the entire areas including the important area and the other areas.
While the technology disclosed in Document 2 utilizes a layout structure of a document, a layout object is transmitted and displayed at fixed high and low resolutions. Thus, depending on a layout object included in a document image, transmission time becomes uneven, i.e., it may take a long period of time or short period of time for transmission. This imparts an unpleasant feeling to the user and can be a cause of stress.
In addition, in the technology disclosed in Document 3, the up-time is determined from a remaining battery capacity and an image is transmitted at a resolution level in accordance with the determined up-time. Thus, for example, a specific area and a viewing speed according to user's preferences cannot be specified, so that this technology has a drawback in that various viewing modes cannot be controlled based on a user's selection.
The problems of the technologies disclosed in Documents 1 to 3 described above are attributed to a point that a user's viewing speed (e.g., a page-turning speed) is not considered at all. Thus, all of the technologies have problems in that they provide an unpleasant feeling to users and cause inconvenience to the users.
Additionally, all of the technologies described above have a problem in that it is impossible to smoothly turn pages at a constant page-turning speed while ensuring the quality of an area of user interest. Further, the transmission speed of a network varies depending on, for example, the type of network. Yet, no consideration is given to ensuring a viewing condition set by a user even for a varied transmission speed.
Accordingly, an object of the present invention is to provide an electronic-document viewing system and a method which allow for comfortable document viewing without imparting an unpleasant feeling to a user.
Another object of the present invention is to provide an electronic-document viewing system and a method which allow for smooth page turning at a constant page-turning speed while ensuring the quality of an area of user interest.
Still another object of the present invention is to provide an electronic-document viewing system and a method which can ensure a viewing condition set by a user, even when the transmission speed of a data transmission network varies.